The present invention relates to electrodeposited copper foil with carrier and to a copper-clad laminate formed from the electrodeposited copper foil with carrier.
Conventionally, electrodeposited copper foil with carrier has been employed as a material for producing printed wiring boards, which are widely used in the electric and electronic industries. In general, electrodeposited copper foil with carrier is bonded through hot-pressing, onto an electrically insulating substrate such as glass-epoxy substrate, phenolic polymer substrate, or polyimide, to thereby form a copper-clad laminate, and the thus-prepared laminate is used for producing printed wiring boards.
Electrodeposited copper foil with carrier resists formation of wrinkles in the copper foil during hot pressing, and therefore prevents generation of cracks in the copper foil, which initiate from wrinkled portions. As a result, bleeding of resin from a prepreg is prevented. Thus, the copper foil with carrier has been attracting attention because these problems can be eliminated, and because foreign matter is prevented from penetrating into copper foil throughout the process of hot-pressing.
Specifically, the electrodeposited copper foil with carrier has a structure such that a carrier foil and an electrodeposited copper foil form a sheet as if surfaces of the two foils were bonded to each other. Such foils are subjected to hot press as they are, and the carrier foil is removed just before the copper foil is etched for producing a copper circuit. Thus, generation of wrinkles in the electrodeposited copper foil during handling or pressing thereof, and surface staining of a produced copper-clad laminate can be prevented.
Carrier foil, this term is used throughout the present description, is used in the form that one surface of the carrier foil is as if bonded to one surface of an electrodeposited copper layer. Copper is electrodeposited on one surface of the carrier foil so as to form a copper foil. Bonding of the carrier foil to the carrier foil is maintained at least until completion of the production of a copper-clad laminate. The carrier foil facilitates handling of the electrodeposited copper foil and is very effective in reinforcing and protecting the copper foil. Therefore, the carrier foil must exhibit a certain level of mechanical strength.
Any material may be used as the carrier foil so far as the material satisfies the aforementioned conditions, and generally, metal foils may serve well as the carrier foil. However, the carrier foil is not limited only to metal foils.
Electrodeposited copper foils with carrier are generally classified into two types; i.e., peelable foils and etchable foils. The present inventors have proposed a peelable electrodeposited copper foil with carrier in which the carrier foil and the copper foil are bonded via an organic release interface, since such a peelable electrodeposited copper foil exhibits remarkably improved releasability of the carrier foil from the copper foil.
However, in recent years, there has been increasing demand for a copper foil which permits easy handling during the etching and stacking processes employed in the production of printed wiring boards from a copper-clad laminate. This is because ever-increasing demand for downsizing of electronic and electric apparatus leads to strong demand for an increase in the number of layers in printed wiring boards; an increase in the density of a circuit formed from copper foil; and an increase in the packing density of mounted devices.
In order to further increase the density of a circuit formed from copper foil and the packing density of mounted devices, copper wirings for forming circuits are made finer and a number of substrates are stacked. Interlayer electrical connection is established by means of contact holes such as through holes (PTH), interstitial via holes (IVH), and blind via holes (BVH), which are formed by making predetermined holes in a printed wiring board. Although hole-making is conventionally carried out by means of a mechanical drill, high-precision processing by means of a CO2 gas laser or the like has been employed in recent years so as to form a fine circuit from copper clad laminate.
Processing with a laser is very advantageous in that fine processing can be carried out with high precision. However, determination of processing conditions is quite difficult because copper foil used in printed wiring boards has a glossy surface and therefore reflects laser beams.